Larvicidal material, including material taken from Bacillus thuringiensis var. Israelensis (Btl) and material taken from Bs (Bacillus sphaericus) has been used to control insects such as mosquitoes by application of the material in the form of a spray or in the form of granules to bodies of shallow water that contain mosquito larvae. Bacillus materials can be added to water in a spray tank in the form of a wettable powder, or in the form of an emulsifiable concentrate (where the material is suspended in a water immiscible oil which includes surfactants that facilitates dispersion in water).
U.S. Pat. No. 3,271,243 (Cords and Fisher, 1963) discloses a stable concentrated bacterial insecticidal suspension. The bacteria, when cultivated in an appropriate aqueous nutrient media, form spores and also form crystallised proteins which are toxic to insects.
US 2004/0185079 (Zomer, filed 2002) refers to a method to control insects by broadcasting a sustained release pesticide granular composition comprising 5-60% of a larvicidal protein, 5-60% floating hollow particles coated with hydrophobic material, 1-25% water-soluble sunscreen pigment and 1-25% of insoluble fibrous matrix. Preferences are noted as follows: (i) a release period of about 30 days, (ii) flotation agent selected from perlite, vermiculite, industry by-products such as feather or peanut shell particles, cellulose by-products such as corn cob and cork-derived materials, (iii) flotation agents to be treated with hydrophobic material such as paraffin, hydrophobic silica, natural fats, oils, (iv) inclusion of larvae feeding stimulants such as fish meal, soy meal, yeast meal), (v) inclusion of 0.1-5% detergents such as alkylpolysaccharides or Tweens, (vi) use of humate as the sunscreen agent, (vii) use of insoluble fibrous matrix from industrial sludges.
The larvicide is most effective at the air-water interface. This generally means having granules that have a low granule density so the granules float to provide an effective concentration of larvicide at the air water interface. However granules with a low density also have low packing density, so that aerial application from aircraft such as helicopters or fixed wing aircraft is expensive due to the limited carrying capacity of aircraft.